To impart lubricative property, water repellency and the like on a surface of a solid, a process for forming a film having good lubricative property on the solid surface from a liquid having a lubricating polymer dissolved or dispersed therein is adopted.
For miniaturization and precision-enhancement of electronic instruments, mechanical devices and parts, it is required that sliding parts or surfaces thereof have a good lubricative property. Especially, for improving sliding property between a hard disk, a miniature disk, a magnetic tape such as a digital audio tape or a video tape, or other magnetic recording mediums, and a head for recording and reading, lubrication with high precision, durability and reliability is required. Thus, to secure, for example, durability and practical reliability of a hard disk, a protective layer such as a carbon layer and additionally a lubricative layer of fluoropolymer are formed on a hard disk. For improvement of performances and miniaturization of cameras, video cameras, business and office machines, medical instruments, vacuuming devices such as a vacuum pump, electronic parts, precision automobile parts, small size motors, ultrasonic motors and micro-machines, formation of a lubricative layer made of a fluoropolymer on sliding parts is widely adopted to attain lubrication with enhanced durability, high reliability and reduced staining property. For an ink-jet recording head, a water repellent film is formed on a surface of the nozzle to secure extrusion stability and directional property of a polar liquid flowing through the nozzle hole.
Many proposals have been made as for the process for forming a lubricative film or a water repellent film on a surface of a solid. For example, a process has been proposed wherein a polymer having an extremely low surface tension such as a fluoropolymer is dissolved in a suitable volatile solvent, various materials and parts are coated with the thus-obtained solution, and then, the solvent is vaporized to form a polymer film.
Another proposal using a solution of a fluoropolymer in a fluorine-containing solvent is known. As for the fluorine-containing solvent, there can be mentioned, for example, freon 113 (Japanese Unexamined Patent Publication (abbreviated to "JP-A") H5-342570) and perfluoro-n-heptane (JP-A H4-211959). However, freon 113 is now not on the market although it has been heretofore used, because of prohibition of production of ozone-depleting substances. Perfluorocarbons such as perfluoro-n-heptane have a poor dissolving power for various materials and cannot be used for the formation of a uniform fluoropolymer film.
A process for forming a film from a polymer dispersion is described in JP-A H3-158884 wherein finely divided particles of polyvinylidene fluoride, phenolic resin or Tosu-pearl are dispersed in a liquid medium selected from isopropyl alcohol, ethyl alcohol, freon 113 and water, and the thus-prepared dispersion is coated on an image-carrier and a contact surface of a member placed in contact with the carrier in an image-forming device, followed by drying the coating. It is described in JP-A H3-158884 that frictional force between the image-carrier and the contact member such as a cleaning blade is mitigated by formation of the polymer film whereby problems such as surface peeling of the blade and non-uniform static electrification on the surface of the image-carrier are solved.
Another process for forming a film from a resin dispersion is described in JP-A H3-197952 wherein a dispersion of a finely divided lubricative powder such as finely divided fluoro-resin powder or a finely divided silicone resin powder in an organic solvent is sprayed onto a surface of an electrophotographic photoreceptor, followed by drying. As examples of the organic solvent, there can be mentioned freon solvents. It is described in this patent that frictional force between the photoreceptor and a cleaning blade for removing a residual toner is reduced by this process and thus a problem of surface peeling of the blade is solved.
However, the dispersions of the finely divided lubricative polymer particles in an organic solvent have a poor uniformity in dispersibility, and thus, the lubricative polymer films formed therefrom have an unsatisfactory effect for frictional force reduction.